At 5:30 AM, 150 years ago this morning, the I Corps of the Army of the Potomac began an attack towards the Dunker Church near the town of Sharpsburg, beginning the bloodiest day in American military history.

At Sharpsburg, the Army of the Potomac had a decisive edge in terms of men and materiel, but suffered the significant tactical disadvantage of being led by George McClellan. Under his command, that army always moved slowly, cautiously, a side-effect of McClellan’s laughable overestimates of Confederate strength. Where one Rebel marched, McClellan always saw three, and his tactical decisions were always made under this catastrophic misapprehension of his opponent’s numbers. McClellan’s fought as much to forestall defeat as to achieve victory, though his delusions of Rebel legions transformed even his minor successes into glorious triumphs, in his mind.

A few days previously, McClellan had come into possession of intelligence describing the exact movements of the Army of Northern Virginia, but his slow movements had allowed the Confederate force to avoid destruction and concentrate across the Antietam. Thanks to the delay, the Rebels were able to recall reserves and reinforcements from a successful action at Harper’s Ferry. McClellan’s slowness and timidity would confound his military fortunes on this day as well.

Satellite imagery of Sharpsburg MD (from Google Maps), with some battlefield features labeled.

Robert E. Lee, commanding the Army of Northern Virginia, knew McClellan’s limitations and weaknesses well. McClellan had forces arrayed all along Lee’s line, and had they all attacked at once the Rebels would have been swept into the Potomac before A.P. Hill could have come up. McClellan, though, would never undertake such an assault, given the risk of the imaginary gray legions placing overwhelming demands on his reserves. Lee knew he could safely shift forces around the battlefield to confront the piecemeal attacks.

The I Corps attacked under the direction of one of the few Union commanders to display any sign of competence that day. Fighting Joe Hooker, who had received his sobriquet as the result of a typographical error, arranged a coordinated attack down the Hagerstown Pike and across the cornfield of David Miller. However, his movements had been observed the previous evening, and the Rebels had positioned the division of Alexander Lawton, supported by some of their best artillery, to greet him.

Shortly after 6 in the morning, the Yankees exited the south end of the Cornfield and into withering fire from lightly-entrenched Confederate forces. The Rebels pressed forward as the Union brigade withdrew, then fell back as supporting units from the I Corps moved in. A seesaw battle for the Cornfield began, with units on both sides losing 60% of their men or more. However, the piecemeal nature of McClellan’s attack allowed Lee to move in new units from elsewhere on the field and commit reserves with confidence, achieving local numerical parity despite the generally overwhelming Yankee forces.

At 7 AM, a division under John Bell Hood charged into the Cornfield, pushing the Yankees back into woodlots north and east of the field. His attack ran too far north, however, and suffered a bloody repulse. Within thirty minutes, the Rebels held the Cornfield and had a lodgement in the East Woods. At this point in the day, most people are still sipping coffee, if they are even awake. In 1862, the Confederate army had lost a third of Starke’s division, half of Lawton’s, and more than half of Hood’s. Hooker’s I Corps had lost more than 2500 men, almost a third of its strength.

Hooker’s troops were too disorganized to press forward, so he called on the XII Corps, briefly led by Joe Mansfield until he caught a bullet in the chest and command reverted to Alpheus Williams. Their initial arrival was disorganized and resulted in a futile attack by several regiments. Then, a skittish Rebel brigade broke and ran from the East Woods, and George Greene’s division turned the flank and swept the Rebels into the West Woods.

Lee, however, knew McClellan too well. From his position close to the front, he could feel the danger and was already committing the divisions of Lafayette McLaws and John Walker to the defense of his left, stripping his right with the confidence that if McClellan mounted an effective attack there, he would still have time to respond. Even this might not have been enough, but the most effective Union commander that day was about to be removed from the conflict. Hooker, riding a conspicuous white horse, was shot through the foot and by 9 AM he was forced to leave the field.

McClellan, commanding from Pry’s farm, a position more than a mile distant from the battlefield, and from which much of it could not even be seen, now committed 2/3 of the II Corps under Edwin Sumner, keeping one of its divisions in reserve to fend off the countless Rebel soldiers should they break through. On his way to the front, Sumner lost even more of his strength, as the division of William H. French lost contact and drifted off to the southwest. Without reconnoitering the ground, and ignoring what he was told by Williams, Sumner decided to take his remaining division, in a tightly massed formation, due west, towards what he believed to be the edge of the Confederate line.

In fact, he was marching north of their lines, and as he entered the West Woods, Rebel soldiers led by McLaws, Jubal Early, and Tige Anderson rolled up his flank and engulfed the division. Massed as they were, the Union soldiers could not turn to make a line of battle. The whole division was chased out of the woods, and the Union flank would have caved in if not for a valiant effort by the recently-named Iron Brigade of John Gibbon, which had already been plenty shot up that morning in fighting on the Pike.

Now the rebels got too aggressive again, and Greene managed another advance, getting a foothold in the West Woods. At this point the Rebels really were in danger of losing their flank, but thanks to McClellan’s piecemeal attack, his hoarding of reserves (especially the Federal cavalry, who were held out of the battle entirely), and Sumner’s incompetence, no troops were left to support an effort to make a further breakthrough.

French’s division, which Sumner had lost some minutes earlier, was advancing towards an eroded roadway leading away almost perpendicularly from the Hagerstown Pike. This Sunken Road made a natural trench, and Confederates commanded by D.H. Hill had fortified themselves there. French’s division approached the Sunken Road over open ground, and the first blast from the Rebels killed almost everyone in the front rank of the Union advance. The division had many rookie troops and became badly disorganized, but long-range artillery fire prevented the Rebels from flanking them. French’s division lost more than 1700 men without any real effect on the Confederate line.

Shortly after 10 in the morning, McClellan released the last of Sumner’s divisions, under Israel Richardson, to attack the Sunken Road, and Lee committed his last reserve force, under Richard Anderson. Anderson was wounded on the way, however, and command of his division was passed to Roger Pryor, who mishandled the advance, creating confusion in the Rebel lines. While the Confederates were able to repel a direct assault by one Union brigade, a second brigade swung around to the south. Fearful of being flanked, and troubled by the confusion, the Rebels broke under another frontal assault and ran. At the other end of the road, enfilade fire and confusing orders compelled the Rebel left to withdraw, and the Federal troops began to advance towards the Hagerstown Pike.

James Longstreet, wearing a carpet slipper rather than a boot on account of a painful blister on his heel, and Hill, however, launched a series of counterattacks that imperiled the Union flank. Although none of them threatened to collapse the Union line, they blunted the advance and compelled Richardson to withdraw to regroup and resupply his troops. Unfortunately at this point Richardson was mortally wounded, and though the Rebel center was in a dangerous state, McClellan’s lack of nerve would prevent him from committing reserves to exploit the opportunity. At the Sunken Road, 5500 Union and Confederate soldiers had died for nothing. It was McClellan’s cowardice, not Rebel blood, that saved the Army of Northern Virginia.

With McClellan reluctant to advance in the center, and his northern flank still disorganized, the responsibility of the offensive fell on Ambrose Burnside and the IX Corps. Just as French’s division had approached the Sunken Road, Burnside had received orders to attack the southern end of the Rebel line across what was then known as the Rohrbach Bridge.

Attacking across the bridge would be foolish because the east side of Antietam Creek had little cover and the west side had a rocky hill that afforded beautiful firing lines. As such, the plan had been to use an attack on the bridge as a diversion while sending Isaac Rodman’s division to ford the creek downstream and flank the Rebels. Alas, the reconnaissance had been incompetently performed, the planned fording point was unusable, and the location and route to a decent ford had to be pleaded out of local farmers. This took Rodman out of the fight for hours.

Burnside assaulted the bridge anyway, and by noon several of his regiments had been shot to bits in indifferently-prosecuted attacks. However, Lee had stripped his right flank to the bone in order to hold off attacks on the left and center of his lines, and had already committed his reserves. With their ammunition drying up, even their dominant defensive position could not hold off the Yankee numbers, and the Confederates withdrew towards Sharpsburg. With the right collapsing, a great victory was at hand, or would have been, if Burnside had any real talent for command. Instead, he allowed the bridge to become a bottleneck and spent hours getting his troops across – hours that the Confederates would put to good use.

Stonewall Jackson made use of the opportunity to arrange a flanking movement by J.E.B. Stuart’s cavalry, as yet uncommitted, to swing around the northern end of the Union line and attack it from the rear. This plan eventually came to nothing, but some of Jackson’s troops turned the delay to decisive advantage. The lull gave A.P. Hill time to arrive with his “Light Division”, so named because it was the largest division in the army at a time when Southerners appreciated irony. Their other name was “foot cavalry”, and this day the Light Division had left Harper’s Ferry at 6:30 in the morning, marching 17 miles to reach the Potomac near Sharpsburg at around 2:30 in the afternoon. This might not seem too impressive to a modern marathoner, but one must keep in mind they did this in formation, carrying several dozen pounds of gear each, without benefit of Gatorade or, in many cases, shoes.

By 3 PM, Burnside had gotten his act together enough to begin an attack, and with A.P. Hill’s men yet to deploy, he faced only the brigades of David R. Jones. Burnside intended to strike towards the Harper’s Ferry Road, cutting Lee off from the nearest ford and putting his army in great danger. Had McClellan committed artillery or men to support the advance this plan might have worked out despite everything. As it happened, however, McClellan was too timid to commit anything, and a whole corps of troops and the entire body of the Federal cavalry continued to doze in the middle of the field, having never once fired a shot.

Burnside’s attack reached Sharpsburg, but he had not received the word that the Light Division was coming up from the south. As Jones’ men regrouped and counterattacked from Sharpsburg, Hill struck the advancing force on the left flank. The Union attack dissolved, and the IX Corps retreated towards the Rohrbach Bridge, soon to be renamed for Burnside. Fresh troops likely would have been able to drive off Hill’s hard-marching division, but McClellan would not release them from the center. The battle ended with Burnside holding a small bridgehead — territory Lee and Hill were content to let him keep.

By 6 in the evening it was all over. More than 23,000 men had fallen dead or wounded during the day’s back-and-forth fighting, and the lines of the opposing armies stood pretty much where they had at dawn, give or take a few hundred yards. At no less than three junctures during the day McClellan could have swept the enemy from the field, but his unwillingness to commit his reserves, coordinate his attacks, or even just properly reconnoiter the battlefield had let those chances get away from him, just as he had dithered away his opportunity to destroy Lee’s army when it was divided in the mountains of Maryland.

By early November, McClellan would be gone, having finally exhausted Lincoln’s patience. Burnside, despite his general bungling of the bridge attack, would be rewarded with command of the whole Army of the Potomac, with depressingly predictable results.

Despite this missed opportunity, the Battle of Sharpsburg (or Antietam, depending on where you grew up) is generally counted a Union victory, if only a minor one. Lee’s threatening attack into Maryland was turned back, and though he inflicted marginally more casualties on the Yankees than he suffered himself, he could afford them less. Still, he got away lightly. With an even marginally competent effort in the battle and the days leading up to it, the Army of Northern Virginia could and should have been destroyed. The Army of the Potomac, unfortunately, had a coward for a commander and a staff of fools. Thus we remember Sharpsburg not as the singular, sparkling victory of a brief and painful war, but a testament to the sad, sick stupidity that caused the war to drag on for four blood-soaked years.

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For further reading on Antietam, I recommend Stephen W. Sears’ Landscape Turned Red, which is a lively account that is very easy to read. McClellan, Sherman, and Grant by T. Harry Williams is a good one for understanding Little Mac.